1. Field of the Invention
The present invention relates to a disposable diaper in which biodegradable non-woven polyester fabric is used as a liquid permeable surface material and as an leakproof backing material. More particularly, the present invention is concerned with a disposable diaper which is not only excellent in mechanical strength, softness, waterproofness, air permeability and feel of touch but is wholly biodegradable.
2. Discussion of the Background
In recent years, disposable diaper is finding remarkably spreading use, and is facing diversified demands in regard to the quality.
Various improvements have been achieved in the constructions of disposable diapers. However, most of disposable diapers consist of a liquid permeable surface portion which contacts with the user's skin and which is generally referred to as "cover stock", a liquid absorbing portion made of fluffed pulp containing high absorbency polymer, and an leakproof backing portion for preventing water leakage generally referred to as "back sheet".
Papers were used in some old-type disposable diapers. Nowadays, however, non-woven cloths made by thermal bond method or spun-bond method are used in most disposable diapers.
On the other hand, leakproof backing material is required to excel in leakproof performance (waterproofness), softness and moisture permeability to release the internal moisture to the exterior, as well as large tear or breakage strength. It is also required not to make rustling noise.
Conventionally, the leakproof backing material has been made of a material such as a film of plasticized polymer such as polyvinyl chloride, low-density polyethylene, polypropylene, polyurethane, ethylene-vinyl acetate copolymer, ethylene-(meta)acrylic acid ester copolymer or the like, or a film which is formed by mixing a filler such as calcium carbonate in the above-mentioned film, stretched the film so as to generate micro-pores, and effecting satin-like embossing on the film.
Thus, in the known disposable diaper, the liquid permeable surface material and the leakproof backing material are not biodegradable, although the liquid absorbing material made of fluffed pulp exhibits biodegradability. Consequently, when the diaper is disposed into the ground, the surface material and the backing material remain without being degraded. For the purpose of complete disposal, therefore, it has been necessary to burn the whole diaper or to separate the liquid-permeable surface material and the leakproof backing material from the top sheet layer for separate disposal.
An object of the present invention is to develop a biodegradable disposable diaper in which a biodegradable liquid-permeable surface material and a biodegradable leakproof backing material are used in combination and which exhibits superior mechanical strength, softness, feel of touch and waterproofness, as well as high productivity. It is also an object of the present invention to develop a biodegradable disposable diaper to which air-permeability is imparted without reducing waterproofness. It is also an object of the present invention to provide a diaper having top layer of an extremely good feel of touch.